This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-159449, Filed May 28, 2001, the entire contents of which are incorporated herein by reference.
The present invention relates to a fixing mechanism which fixes a toner image (image) on a fixation member in an image forming apparatus such as an electro-static process copying machine or a laser printer, and more particularly to a fixing mechanism using an induction heating method.
A fixing mechanism incorporated in a copying apparatus using an electrophotographic process heats and fuses toner which is a developer formed on a fixation member and fixes the toner on the fixation member. As a method for heating the toner which can be used in the fixing mechanism, a method using radiant heat from a halogen lamp is widely utilized.
As the method using the halogen lamp as a heat source, there is extensively used a structure in which a pair of rollers are provided so as to be capable of providing a predetermined pressure to the fixation member and the toner and a cylindrical halogen lamp is arranged in an inner space of at least one of the rollers as a hollow cylinder. In this structure, the roller having the halogen lamp arranged therein forms an action portion (nip) at a position where it is brought into contact with the other roller and provides the pressure and heat to the fixation member and the toner guided to the nip. That is, the fixation member, namely, paper is passed through a fixation point which is a pressure welding portion (nip) between a heating roller to which the lamp is provided and a pressure roller which rotates in accordance with the heating roller, and the toner on the paper is fused and then fixed onto the paper.
In the fixing mechanism using the halogen lamp, light and heat from the halogen lamp are radiated in the circumferential direction of the heating roller and the entire heating roller is heated. In this case, taking the loss when light is converted into heat and the efficiency or the like when warming the air in the roller and transmitting the heat to the roller into consideration, the heat exchange effectiveness is 60 to 70%. Further, it is known that the heat efficiency is low, the power consumption is large and the warming-up time is prolonged.
In order to solve the above-described problems inherent to the heater fixation, as shown in Jpn. Pat. Appln. KOKAI Publication No. 9-258586 or Jpn. Pat. Appln. KOKAI Publication No. 8-76620, there is proposed a fixing mechanism using a technique of induction heating.
Jpn. Pat. Appln. KOKAI Publication No. 9-258586 discloses a fixing mechanism which passes a current to an induction coil obtained by winding a coil around a core provided along a rotational axis of a fixing (metal) roller and generating an induction current to the roller in order to heat the metal roller itself.
Further, Jpn. Pat. Appln. KOKAI Publication No. 8-76620 discloses a fixing mechanism which has a conductive film accommodating therein magnetic field generating means and a pressure roller pressed against the conductive film and fixes the toner on a recording medium carried between the conductive film and the pressure roller onto the recording medium by causing the conductive film to generate heat.
For the purpose of reducing the warming-up time, in the fixing mechanism having a thinner heat roller or the fixing mechanism which adopts a belt or the like, a temperature hysteresis distribution is apt to appear on the heat roller depending on a size of the paper inserted and only a part through which the paper has passed consumes the heat energy. Therefore, irregularities in temperature are generated, and hence temperature control or a partial heating method which does not depend on the paper size is required in the fixing apparatus to which induction heating is applied in particular.
It is an object of the present invention to provide a fixing mechanism including an electromagnetic induction coil, which does not generate a temperature distribution in the heat roller or irregularities in temperature due to a size of the paper to be carried.
According to the present invention, there is provided a heating mechanism comprising:
a first coil body and a second coil body, each coil body of which increases a temperature of an object;
a first temperature detection mechanism and a second temperature detection mechanism, the first temperature detection mechanism detecting a temperature which is a result of increase in temperature of the object when a predetermined output is supplied to the first coil body, and the second temperature detection mechanism detecting a temperature which is a result of increase in temperature of the object when the predetermined output is supplied to the second coil body; and
an output control mechanism capable of alternately supplying the predetermined output to each of the first coil body and the second coil body;
wherein the output control mechanism continuously supplies the predetermined output to the first coil body until the first temperature detection mechanism detects that a temperature in an area of the object which is increased by the first coil body reaches a predetermined temperature as a result of increase in temperature of the object by the first coil body, and does not supply the predetermined output to the second coil body while the predetermined output is supplied to the first coil body.
Further, according to the present invention, there is provided a fixing mechanism comprising:
a first coil body which increases a temperature of an object and a second coil body which increases a temperature of the object;
a first temperature detection mechanism which detects a temperature which is a result of increase in temperature of the object when a predetermined output is supplied to the first coil body, and a second temperature detection mechanism which detects a temperature which is a result of increase in the object when the predetermined output is supplied to the second coil body; and
an output control mechanism which supplies the predetermined output to each of the first coil body and the second coil body, the output control mechanism being capable of alternately supplying the predetermined output to either of the first coil body or the second coil body or simultaneously supplying the predetermined output to both the first and second coil bodies,
wherein, in case of supplying the first predetermined output and the second predetermined output to the first coil body and the second coil body, the output control mechanism gradually increases a magnitude of the first and second predetermined outputs at fixed intervals until either the first predetermined output or the second predetermined output is supplied to at least one of the coil bodies from the off state of all the respective coil bodies and heating force output from the coil body to which that output is supplied reaches a predetermined magnitude.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.